The M26 has been in development at the U.S. Army's Soldier Battle Lab since the late 1990s. The idea was to provide soldiers with lightweight accessory weapons which could be mounted under the standard issue M16 rifle or M4 carbine.

The XM26 is a modular Accessory Shotgun System (MASS). It can be used as an under-barrel shotgun attachment. XM26 was first named as Lightweight Shotgun System (LSS). Now it is officially named as XM26 Modular Accessory Shotgun System (MASS).